This invention relates to an epoxy resin composition, particularly an epoxy resin composition for encapsulating semiconductors and semiconductor elements such as diode, transistor, IC, and LSI elements, which composition is superior in low strain stress, high resistance to thermal shock and high-temperature properties.
In the field of electronic parts today, it is desirable to provide miniaturized, light-weight parts and multifunctional parts by providing the elements in high density, large-size and combinations of the elements. In such electronic parts, particularly semiconductors, there has been widely employed an encapsulating process using encapsulating resins. Various improvements of such encapsulating resins have been demanded.
Conventionally, as the semiconductor encapsulating resin, there have been employed materials such as epoxy, silicon, phenol, diallyl phthalate and the like. Among such materials, the epoxy resin molding material using the phenol type novolak resin as a hardener is superior to other encapsulating resins in points of having in combination adherability to the material to be encapsulated and electrical properties, and have been used extensively.
A transfer molding process is generally used for resin encapsulation of the semiconductor elements. However, in such a process, the difference in the coefficient of thermal expansion between the elements made of inorganic materials and the resin is so tolerable that it has a drawback that a high strain stress occurs when a sudden change in the temperature takes place during or after the molding process. The conventional epoxy resin type molding material has particularly suffered a large strain stress, and when it is directly molded without applying a flexible protective coat to large element dice, the element dice suffer cracks and/or the bonding wires break. Recently, ultra-thin, resin-encapsulated semiconductors which are small and light-weight have suffered from the defect that the encapsulating resin itself cracks due to the strain stress and loses its encapsulation function. To remedy such defects, the development of resins which have a small strain stress and which do not form cracks has been desired. As a method to reduce the strain stress of the encapsulating resin, there are (1) a method of lowering the coefficient of thermal expansion of resin to nearly that of the inorganic materials, and (2) a method of lowering the elastic coefficient.
The above method (1) is generally carried out by adding to the resin an inorganic filler having a low coefficient of thermal expansion. By this method, the encapsulating resin can be lowered in the coefficient of linear expansion but its elastic coefficient increases. Therefore, the lowering of the strain stress is not sufficient. The above method (2) is conducted by adding to the resin a flexibility imparting agent. Conventionally, there have been used as the flexibility imparting agent diglycidyl ether of bisphenol A having a long side chain and bisepoxy of a long chain, such as polypropylene glycol diglycidyl ether, and recently there have been used reactive liquid rubbers such as low-molecular-weight polybutadiene having on the ends carboxyl group, amino group, etc., and their copolymers. However, when such flexibility imparting agents are added until the strain stress is sufficiently decreased, there are caused drawbacks, such as lowering of the mechanical-strength and the glass transition point. As a result, the thermal shock properties and the high-temperature properties are greatly affected.